1. Fast and Reliable Route Discovery Protocol Considering Mobility in Multihop Cellular Networks Hyun-Ho Choi and Dong-Ho Cho Wireless Pervasive Computing, 2006 1st International Symposium on, 16-18 Jan. 2006, Page(s):6 pp. Yu-Wen Chiang

2. 2 Outline  Introduction  Related Works  Proposed Route Discovery Protocol Conventional Route Discovery Proposed Route Discovery Cross-layer Design  Simulation Results and Discussions  Conclusion

3. 3 Introduction  In multihop network environments, system performances are affected by various factors such as mobility, battery power, coverage, interference, and density of nodes.  The mobility is likely to be a major factor.  In order to minimize the effect of mobility, we focus on a fast route discovery protocol.

4. 4 Introduction  In pure ad hoc networks, the routing is a very difficult issue due to the mobility of users and the lack of central control.  Routing in multihop cellular networks, a central AN (access node) which is the common source in the downlink and the common destination in the uplink.  The central AN transmits pilot signals periodically, every node in the network can measure the signal power from its AN.  This signal power can be used as an effective link cost between each node and its AN.  Therefore, our proposed routing protocols consider this link cost for faster and more reliable route discovery in the multihop cellular network environments.

5. 5 Related Works  [2] and [3] introduce three strategies to select a proper RN for two-hop relaying in cellular networks: minimum total pathloss least maximum pathloss minimum relaying hop pathloss.  They consider only two-hop relaying and take no thought of the mobility of nodes.  Mobile ad hoc networks are generally categorized as: proactive routing protocols reactive routing protocols  These ad hoc routing protocols require the frequent broadcast of control messages, which may induce channel overhead and long route discovery time. [2] V. Sreng, et al., "Coverage enhancement through two-hop relaying in cellular radion systems," IEEE Wireless Commun. and Networking Conf: (WCNC'02), vol. 2, pp. 881-885, Mar. 2002. [3] V. Sreng, et al., "Relayer selection strategies in cellular networks with peer-to-peer relaying," IEEE Vehicular Technology Conf:, vol. 3, pp. 1949-1953, Oct. 2003.

6. 6 Related Works  [6]-[8] consider the use of RNs to perform the fast and seamless handover.  However, they focus on only the handover procedures through multihop relay and do not consider the detailed discovery procedures of RN needed for handover. [6] H. C. Chao and C. Y. Huang, "Micro-mobility mechanism for smooth handoffs in an integrated ad- hoc and cellular IPv6 network under high- speed movement," IEEE Trans. Veh. Technol., vol. 52, pp. 1576-1593, Nov. 2003. [7] H. H. Choi and D. H. Cho, "TAKEOVER: a new vertical handover concept for next-generation heterogeneous networks," in Proc. IEEE Vechicular Technology Conf:, June 2005, to be published. [8] Ming He, et al. "Ad hoc assisted handoff for real-time voice in IEEE 802.11 infrastructure WLANs," IEEE Wireless Commun. and Networking Conf: (WCNC'04), vol. 1, pp. 201-206, Mar. 2004.

7. 7 Proposed Route Discovery Protocol  We deal with the two-hop relay process in which the MN finds one RN among neighbor nodes (NNs) within its coverage.  We use the pathloss on each link as a criterion for RN selection.  Because choosing an RN (relay node) based on the physical distance is not practical due to the fading and shadowing effects, and every MN can recognize the pathloss from the received signal strength.

8. 8  PL 1,i and PL 2,i : the pathlosses in dB associated with the first (between MN and NN j ) and the second (between NN i and AN) hops, respectively, along the i th route.  PL 2,MN : the pathloss from AN to MN  In the proposed route discovery protocols, the minimum total pathloss selection method is used to select an RN.

9. 9 Proposed Route Discovery Protocol - Conventional Route Discovery  We adopt the CSMA/CA (carrier sense multiple access with collision avoidance) mechanism as the MAC layer protocol.  We define two kinds of control message used for the route discovery process: Relay Request (RREQ) : a broadcast message to request the value of PL 2,i from NN i. fields: Relay Reply (RREP) : a reply message about the RREQ. fields:

10. 10

11. 11 Proposed Route Discovery Protocol - Proposed Route Discovery (inhibit access control (IAC))  The reply of NN whose PL 2,i is larger than PL 2,MN is inhibited because it cannot have an effect on the RN decision. CW (contention window)

12. 12 Proposed Route Discovery Protocol - Proposed Route Discovery (priority access control (PAC))  The RREQ does not contain the pathloss field for PL 2,MN, so it does not use the inhibit access control.  Early stop (ESTOP) message:  When the ESTOP is sent is decided by the MN, according to the density of NNs. CW (contention window)

13. 13 Proposed Route Discovery Protocol - Proposed Route Discovery (priority access control (PAC))  For the prioritized backoff, the value of priority and the size of new contention window (CW) are calculated as :  C : a constant to make the average of priority be unity.  PL max : the maximum pathloss decided by MN's coverage  priority : the ratio of PL 1,j measured from receiving the RREQ  we use simple priority scheme by differentiating the initial window size (CW min ), which is multiplied by the calculated priority

14. 14 Proposed Route Discovery Protocol - Proposed Route Discovery (hybrid)  It uses the inhibit access control and the priority access control.

15. 15 Proposed Route Discovery Protocol - Proposed Route Discovery (hybrid)  RREQ contains the PL 2,MN and the priority is calculated by two pathloss costs, PL 1,j and PL 2,j, as follows:

16. 16 Proposed Route Discovery Protocol - Cross-layer Design

17. 17 Simulation Results and Discussions  The basic MAC operation is based on IEEE 802.11 system using CSMA/CA protocol.

18. 18 Simulation Results and Discussions

19. 19 Simulation Results and Discussions

20. 20 Simulation Results and Discussions

21. 21 Simulation Results and Discussions

22. 22 Simulation Results and Discussions

23. 23 Conclusion  Simulation results show that the proposed schemes can achieve faster route discovery and more reliable route setup compared with the conventional rout discovery scheme.  These proposed route discovery protocols can be applied as an effective routing solution in multihop cellular networks taking into account the mobility.